The invention concerns a device for damping yaw in a trailer on highway vehicle consisting of a motor vehicle drawing a trailer, said device also constituting a safety feature in the event the coupling breaks.
More specifically, it is designed to improve the traction of a highway vehicle consisting of a motor vehicle pulling a tractor with a central axle, also called a balanced trailer.
The risks and dangers associated with yawing trailers during descent at certain speeds are well-known.
These conditions can even cause the trailer to tip or shift sideways, known as being xe2x80x9cjackknifedxe2x80x9d.
A number of devices for limiting yawing motion already exist.
They consist mainly of telescoping lateral arms with damping effects. These arms are attached along the coupling on either side with a ball and socket connection at one extremity on the rear of the vehicle, and are attached to the coupling with a ball and socket connection at the other extremity.
These arms are sufficient to limit small amplitude movements, but large trailers carrying heavy loads remain susceptible to danger.
The object of the invention is to damp and thus limit yaw amplitude by the trailer in a unit consisting of a motor vehicle drawing a trailer. The means according to the invention also constitutes a safety device which forms a temporary connection if the coupling breaks.
To achieve this objective, the damping mechanism comprises a rigid or flexible curvilinear damping track which is acted upon by a friction device attached at the end of the shaft, with either end of the track extending into an articulated or non-articulated connection joining a fixed portion of the rear of the motor vehicle. The friction device consists of flat friction pieces which are placed in contact with the surfaces of the curvilinear track by a force pushing the structures together. The intensity of the push varies, allowing the degree of damping to be adapted according to need. Adaptation occurs automatically and simply, by associating the pushing force with the trailer""s pneumatic suspension and/or to the speed of the vehicle.
In the case of a vehicle without any pneumatic suspension system, either vehicle speed alone is used, or a specialized sensor is used to determine the extent of the trailer""s cargo.
A device for limiting yawing motion is already known, consisting of a section of metal disc and a bracket attached to the trailer""s shaft, equipped with two friction slides. These slides are firmly pressed on either side by the disc using a flexible force device to form a friction brake against the pivoting motion of the shaft in relation to the vehicle and thereby limiting the yawing motion of the trailer.
When nearly worn out, the damping effect achieved with this system is of predetermined intensity dependent only upon the force exerted by the flexible force upon the friction slides and thereby on the sector of track.
With the damping device according to the invention, the force pressing the friction structures against the curvilinear track is not constant. It varies, making the degree of motion absorbed a function of the weight carried by the trailer and/or its speed. It is known that the heavier the cargo on the trailer, the more likely there will be yawing of the trailer and the greater the danger, since the trailer""s inertia increases. The device of the present invention advantageously increases the damping effect in this situation. Actually, the larger the load in the trailer, the greater the pressure exerted on the suspension, and the harder the yawing devices press the friction structures against the curvilinear track, thus increasing friction.
Conversely, when the trailer is empty or carrying a light load, the trailer""s inertia decreases. In this case, less damping suffices. The suspension elements are not pressured as much and the device of the invention that depends upon the suspension elements thus decreases the force exerted on the friction devices, thereby decreasing friction and damping intensity. These variations are obtained simply, quickly, and are completely automatic.
It is also known that speed increases yawing motion. Therefore, both speed values and the amount of pressure on the suspension system can be used to form the basis of an improved control system.
It is also possible to limit yawing by using one or the other of these variables. Obviously, if there is a different type of suspension system, pneumatic control is not possible and a specialized sensor needs to be used if the trailer""s load is used as a basis for the system.
Adapting the intensity of yaw damping to the weight being hauled and/or to vehicle speed decreases wear on the friction structures and thus prolongs the life of the device.
In the same way, yaw damping intensity can also be varied automatically as a function of road conditions, that-is, the difficulties in terrain which the vehicle encounters and the constraints imposed: acceleration, braking, centrifugal force, etc.
The device of the invention has an additional feature: due to the use of a gripping element, maintenance is greatly facilitated; for example, when replacing friction plates and coupling or uncoupling the trailer. With the prior art yaw reduction system, in order to perform the connecting and disconnecting operations, it was necessary to combat a permanent flexible recall force, such as a spring. With the device of the invention, it is only necessary to release the gripping pressure and these operations can be performed effortlessly.
Furthermore, if a pneumatic device is used to press the friction devices together, the invention automatically compensates for the play caused by wear on the friction structures by adapting the pressure applied to the pneumatic activator.
In the latter instance, the nature of fluid pneumatic energy provides a certain progression or reduction in the application of force due to the pneumatic effect accompanying each action.